BACKGROUND: An inverse relationship between vitamin D supplementation and C-reactive protein (CRP) and hypertension has been reported, mostly through observational data. This inverse relationship, however, has not been confirmed in randomized controlled trials (RCTs). A meta-analysis of RCTs is needed to provide more robust evidence. OBJECTIVE: This systematic review of RCTs was conducted to assess the effect of vitamin D supplementation on CRP, systolic blood pressure (SBP), and diastolic blood pressure (DBP) in postmenopausal women. METHODS: Four databases (PubMed, Web of Science, Embase, and Scopus) were systemically searched to identify relevant RCTs published in international scientific journals up to January 2023. Changes from baseline and SDs of CRP, SBP, and DBP were compared between postmenopausal women who received vitamin D supplementation and those who did not (controls). These parameters were applied to compute the overall effect sizes using the random-effects model. Data were summarized as mean difference (MD) with 95% CI. Heterogeneity among arms was scrutinized using the Cochrane's Q test and I2 statistic. Publication bias was judged by means of funnel plots and Egger's test. RESULTS: Seven studies with 6 arms on CRP, 6 arms on SBP, and 6 arms on DBP were included in the meta-analysis. Combined effect sizes suggested a significant effect of vitamin D supplementation on CRP (MD = -0.65 mg/L; 95% CI -0.93 to -0.37 mg/L; P < .001). In addition, CRP concentrations were significantly reduced after vitamin D supplementation in studies with a duration of more than 3 months (MD = -0.91 mg/L; 95% CI -1.37 to -0.45 mg/L; P < .001) and studies involving doses of ≤1,000 IU/d (MD = -2.10 mg/L; 95% CI -2.51 to -1.68 mg/L; P < .001). Vitamin D supplementation did not reduce SBP significantly (MD = -1.06 mm Hg; 95% CI -2.43 to 0.30 mm Hg; P = .127) and DBP (MD = 0.003 mm Hg; 95% CI -0.86 to 0.86 mm Hg; P = .994) levels compared with control groups. CONCLUSIONS: This meta-analysis concluded that vitamin D supplementation is associated with reduced CRP concentrations among postmenopausal women.
